D1 receptors may play an important role in mediating cocaine's addictive properties. We are proposing to use our laboratory model of repeated dose cocaine self-administration to assess the potential efficacy of the D1 receptor antagonist, SCH39166, for the treatment of cocaine dependence. Non-treatment seeking cocaine abusers will live on the hospital unit and will be maintained on placebo and SCH39166 each for 8 days to determine if the medication alters cocaine's reinforcing effects.